Inactivation of ADP-ribosylating toxins has been attempted by using cross-linking agents such as formaldehyde and glutaraldehyde. Cryz et al., "Effect of Formalin Toxoiding on Pseudomonas aeruginosa Toxin A: Biological, Chemical, and Immunochemical Studies," Infec. and Immun., 32, No. 2, 759-768, May 1981 describe such a toxoid. Two problems with some such toxoids have been reversion to the toxic form and loss of antigenicity and immunogenicity. The possibility of their reverting to the toxic state effectively precludes ever obtaining human antisera from such toxoids or their use as active vaccines.